Arrangement for producing relaxation oscillations



NW. 30, 1937. K. SCHLESINGER 1 ARRANGEMENT FOR PRODUCING RELAXATION OSCILLATIONS Filed 001;. I51. 1933 WWW.

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Patented New. so, 1937 area-m2 BRRANGEWNT EDR PRODUCING RELAX- A'IL'IQN @SCKILATIIQN S Kurt Schlesinger, Berlin, Germany Application o tensia1, 1933, Serial No. 696,065 in Germany November 4, 1932 3 Claims.

In the reproduction of television images, and more particularly those images which show characteristics with relatively large, straight, horizontal bounding lines, appreciable curvatures frequently take place, so that the image is reproduced in completely distorted fashion. It may be ascertained that a straight bounding line disposed transversely to the line direction appears appreciably curved when the line tilting portion of the relaxation oscillation apparatus is adjusted approximately 1% too early or too late as compared with its required frequency.

Heretofore it has been assumed that the curvatures are produced by a corresponding error in the transmission of the time marks from the transmitter to the receiver.

In contradistinction thereto it has been found by the applicant that the known relaxation oscillation apparatus, even in a condition of free relaxation oscillations, cannotbe adjusted, or only with extreme difiiculty, in such fashion that the ignition points are sumciently equi-distant, i. e., that the irregular and disturbing displacement of the time of ignition is caused by the construction of these known relaxation oscillation apparatus themselves.

Careful investigations have shown that when using highly sensitive relaxation tubes, for example of the grid-controlled hot-cathode type, the sharpness of controlof which in operation amounts to approximately .1 volt amplitude of the grid potential, a superposed disturbing amplitude may lead to distortion of the image even if the same is only in the order of 10 volts. In consequence particular dimculties occur if an attempt is made to operate tubes of this nature from the mains. Since for various reasons in the grid circuit of these tubes a very high resistance has to be inserted, the smallest capacitative or galvanic coupling of the grid lead with any other circuit conveying humming potential is sufiiclent to produce disturbances. In this connection humming potentials are understood tofbe potentials of the network frequency or harmonics thereof.

It has been found that distortion of the contents of the image is occasioned by the following sources of error:

1. Disturbing potential at the scanning grid.

'2. Unsuitable construction of the transmission members from the amplifier output to the Braun tube.

3. Minimum ripple of the charging currents.-

The subject matter of the invention is an arrangement for producing relaxation oscillations,

which does not reveal the sources of error referred to, and which moreover permits to exchange the relaxation tubes without variation in the frequency.

According to the invention, all conductor portions connected with the grid are enclosed, for example by fitting the same into a completely closed screening tube. The bulb itself of the glow lamp is preferably metallized, and passed to earth. When making use of indirect heating, it is desirable to earth the centre of heating. Further, in this case the filament is constructed and arranged in such fashion that the same 'is screened ofi as completely as possible by the equipotential surface against the discharge space. V

In lieu of screening off all conductor portions which are connected with the grid, the grid, in accordance with the invention-particularly in the case of television apparatus, which operate with a constant line change frequency, which is pm high as compared with the frequency of the mains-may be earthed through the medium of a switching element, which possesses as small a resistance as possible in respect of the mains frequency and the adjacent low frequencies, whilst its (frequency-dependent) resistance is as high as possible as regards the line basic frequency and the harmonics thereof. The switching element may consist of a choke, a coil connected in series with a condenser and tuned to the frequency of the mains, or the like. The choke should be connected with the grid in the shortest way, and if necessary screened oil.

The time constant of the output lead line of the line change'oscillation generator is selected in such fashion, that this lead line does not transmit, or transmits only very poorly, a frequency lower than the basic line frequency. The time constant of the output lead line of the image change oscillation generator is selected in such fashion that the latter allows quite well the passage of the image change frequency, but prevents the penetration of high frequency from the line relaxation generator.

The charging currents of the two relaxation generator units are each steadied per se by a separate reaction member. In this manner it is possible to overcome completely the ripples of the charging currents.

F A form of embodiment of the arrangement according to the invention is illustrated by way of example in the drawing.

' In the latter I and 2 are two grid-controlled gas-filled tubesofwhich l serves for producing the line change-relaxation oscillation, for exchange relaxation oscillation, for example 25 1 cycles. The appertaining discharge. condensers are designated 3 and l, with the charging resistances 5 and 6 and the frequency-stabilizing resistances 1 and 8. The manner of operating is such as to charge condensers 3 and l respectively at a constant rate with direct potential and to discharge them by means of the glow discharge tubes l and 2 respectively suddenly after a corresponding ignition potential has been reached. For producing the operating potential there is employed the mains-connection apparatus 9 which, supplies the common anode potential, and steadies this potential (down to the extent of a remaining permissible ripple 01' up to 5%) through the medium of a mains choke III in conjunction with the two condensers H and I2. The same mains apparatus generates the grid bias for the amplifiers of the two relaxation os-v cillation portions. This bias requires to be a very even one. Any interference between the two relaxation oscillation portions for image and line frequency should be avoided at this point, as otherwise the length of line would vary dependent on the height of the image- For this reason the resistance I3, at which the grid bias of the power amplifiers is tapped, is disposed, between the two steadying condensers II and I2 in the manner shown, as the same is then no longer traversed only by a small part of the amplified relaxation currents, these being conducted mainly over the condenser l2. The grid bias is also additionally steadied by the resistance l4 and'the condenser IS. The grid bias of the power amplifiers l6 and I1 is accordingly fixed. Since, however, in the arrangement according to the invention, these amplifiers perform, in. addition to the amplification, also an anti-distorting function, are intended to operate in the lower bend of their characteristic, and adiustability of the working point is required. According to the invention, pentodes are employed as amplifiers l6 and IT. The correction is adjusted at the screening grid. For this purpose the screening grid is connected'with the anode potential line through the medium of variable high ohmic resistances l8 and 20 adjusted once for ever to give an optimum of linearity. The

elements may Joe dimensioned, for example, as

follows: In the line amplifier: resistance I8, 300,000 ohms, condenser 19, 1 mi.; in the imagechange amplifier: resistance 20, 300,000 ohms,

condenser 2|, 10 mi. In place of the large and accordingly expensive condenser 2| there may be provided with advantage a suitable stabilizing glow discharge path.

the cathode ray of the Braun tube. The essential element is the dynamic working resistance at the Braun tube, 1. e., 22 in the case of the line portion, 23 in the image portion. This resistance should not exceed a critical maximum value of approximately 100,000 ohms and if a regulation of the size of the image is desired at all, it must be carried out as a potentiometer. The output lead line of the line, relaxation oscillation generator 24-22 is provided, in accordance with the invention, with such a small timeconstant that it is not able to transmit a frequency lower than the basic line frequency. The condenser 24 is accordingly made very small: for example, 24 equal to about 1,7.10 F in conjunction with 22 equal to 100,000 ohms corresponding with a time constant of 10-- seconds.

The corresponding system in the imageechango portion consists of the condenser 25 and the potentiometer 23 on the one hand and the resistance.

26 and condenser 21 on the other hand. The por-- tion 2523 must allow the image-change frequency to pass well, for example-25 equal to 2 m1'., 23 equal to 100,000 ohms. The small resistance 26 and condenser 21 have the object of preventing high frequency from penetrating from the line change portion into the television tube.

According to the invention, the grid of the tube I is connected to earth over an element, for example the choke 28, which has in respect of the mains frequency and similar low frequencies an exceedingly small impedance, whilst its impedance in respect of the basic line frequency and harmonics thereof is as great as possible. In place of the choke shown, which solves the problem in the most simple fashion, it is also possible to employ the series connection of a condenser and a coil, which are tuned to the mains frequency, and the like. The choke 28 requires to be connected with the cathode of I, or the resistance 1, in the shortest fashion, and it must be avoided that the connecting wire is also traversed at the same time by powerful unsteady currents from other parts of the apparatus. The feed of the synchronizing potential takes place through the medium of the condenser 29, which is intended to form in conjunction with the grid choke a filter chain against frequencies lower than the line harmonics. Particular attention should be paid to the fact that the grid choke 28 is also not affected by the least magnetic alternating fields. The same ifmecessary should be screened on and armoured. It may also be constructed in the form of a toroid or the like.

According to the invention, the charging currents of the two units are each steadied per se by a separate reaction member. In the line change osci llation generator there are employed for this Purpose the resistance 30 of 100,000 ohms and the condenser 3| of 1 mf., and in the imagechange oscillation generator the similarly dimensioned arrangement 32-33. Primarily these members serve for overcoming the smallest rip- The frequency-stabilizing resistance 1, or 8 (in 1 the order of a few thousand ohms) is constructed in the form of an externally operable potentiometer preferably having a limited angle of rotation. If the resistance is decreased, the relaxation amplitude also decreases, whilst the frequency increases, and vice versa. In this manner the required frequency may be adjusted without difficulty upon the fitting of a new glow tube-which possesses varying constants. It may be shown that the stabilization against fluctuations in the mains is maintained automati= cally when the required frequency is adjusted in this fashion. The resistance 34 and the condenser 35 serve for filtering the long impulses ingly of the production of television images free of curvature.

I claim: a

1. In a television arrangement comprising a relaxation oscillation generator for producing the line deflecting voltage, a, mains supply apparatus for supplying said relaxation oscillation generator from the commercial mains, said generator including a gas-filled discharge tube. having hot cathode, grid and anode, an impedance being connected between said'grid and said cathode, said impedance having a low apparent resistance with respect to the frequency of said commercial mains and a great apparent resistance with respect to the frequency of said line deflecting voltage.

paratus for supplying said relaxation oscillation generator from the commercial mains, said generator including a gas-filled discharge tube having hot cathode, grid and anode, a choke being connected between said grid and said cathode, said choke having a low apparent resistance with respect to the frequency of said commercial mains and a great apparent resistance with respect to the frequency of said line deflecting voltage. I

3. In a television arrangement comprising a relaxation oscillation generator for producing the line deflecting voltage, a mains supply apparatus for supplying said relaxation oscillation generator from the commercial mains, said generator including a gas-filled discharge tube having hot cathode, grid and anode, an impedance being connected between said grid and said cathode, said impedance having a low apparent resistance with respect to the frequency of said commercial mains and-a great apparent resistance with respect to the frequency of said line deflecting voltage, and screening means, said impedance being encased by said screening means.

- KURT SCHLESINGER. 

